(P 356) RADIATION PRACTICE PATTERNS AND OUTCOMES IN ADOLESCENT YOUNG ADULT PATIENTS WITH VISCERAL NON-RHABDOMYOSARCOMA SOFT TISSUE SARCOMA

Objective: We sought to identify radiation therapy (RT) practice patterns and outcomes in adolescent and young adult (AYA; 15-39 years) patients with visceral non-rhabdomyosarcoma soft tissue sarcomas (NRSTS).

Methods: We used the California Cancer Registry (CCR) to identify AYA patients diagnosed with visceral (including thoracic, gastrointestinal, retroperitoneal, gynecologic, genitourinary, nervous system, and other) NRSTS (2004-2018) who had undergone surgical resection. Kaplan-Meier methods estimated sarcoma-specific survival. Multivariable logistic and Cox proportional hazard regression examined factors associated with radiation treatment and sarcoma-specific survival, respectively. These factors accounted for known sociodemographic and clinical characteristics, presented as odds ratios (OR) and 95% Confidence Intervals (CI). Factors included age at diagnosis, sex, race/ethnicity, neighborhood socioeconomic status, insurance status at diagnosis, treatment, tumor size, tumor histology, nodal status, metastatic status, primary disease site, and surgical margin. Cox proportional hazards model identified factors associated with sarcoma specific survival, with results presented as hazard ratios (HR) and 95% CI.

Results: Of the 433 AYA patients with visceral NRSTS, the majority were older (26-39 years, 75.1%), female (64.9%), Hispanics (43.2%), had private insurance (60.7%), and non-metastatic NRSTS (72.1%) at diagnosis. Approximately half of all patients (46.0%) received chemotherapy and 31.9% received RT. Most patients who received RT were treated post-operatively (79.4%) with 5040cGy or less (73.5%). Disease site location was associated with whether patients were treated with preoperative RT in comparison with post operative RT (p=0.0163). In multivariable analysis, patients with undifferentiated NRSTS were more likely to receive RT (Odds Ratio (OR) 2.59, 95% Confidence Interval (CI) 1.13-5.92). Patients with larger tumor sizes showed a trend towards statistical significance with RT (size 10.1-15cm: OR 2.21, 95% CI 0.94-5.18 and >15cm: OR 2.38, 95% CI 0.96-5.90). Overall, 5-year sarcoma-specific survival was 50.4% and it was lowest for patients with metastatic vs non-metastatic disease (17.0% vs.60.7 %, p< 0.001). Sarcoma-specific survival differed by disease primary site, with thoracic tumors having the lowest 5-year sarcoma-specific survival (32.4%), whereas genitourinary tumors had the highest (74.5%). A Cox proportional hazards model identified that patients receiving treatment with chemotherapy (HR 1.84, 95% CI 1.30-2.59) or RT (HR 1.57, 95% CI 1.14-2.14) had worse survival compared with patients who did not receive these therapies. Additional factors associated with worse survival include Public insurance /Self Pay status (HR 1.50, 95% CI 1.07-2.10), larger tumor size (size 10.1-15cm, HR 2.39 95% CI 1.53-3.74, size >15cm HR 2.18, 95% CI 1.34, 3.53), thoracic disease site (HR 2.53, 95% CI 1.35-3.08), positive surgical margin status (HR 1.87, 95% CI 1.20, 2.89), use of chemotherapy (HR 1.84, 95% CI 1.30, 2.59) and use of radiation therapy (HR 1.57, 95% CI 1.14, 2.14). Kaplan Meier analysis demonstrated no difference in 5-year sarcoma-specific survival for patients receiving RT versus those who did not when stratified by stage.

Conclusion: AYA patients with visceral NRSTS have poor outcomes, with half of the patients surviving at 5 years. Less than one third of patients received RT, which was usually postoperative and to doses < 5040cGy. Further investigations are needed to identify the optimal timing of radiation treatment and which patients might benefit from optimizing local control using radiation therapy, such as patients with thoracic disease location, who had the worst prognosis in this study.